She repeated her husband's call for "both sides" to work on immigration reform as a solution. However, fact-checkers point out that the policy was introduced by Mr Trump's attorney general and does not require congressional action to be stopped.

Earlier Mrs Trump said she "hates to see children separated from their families and hopes both sides of the aisle [Republicans and Democrats in Congress] can finally come together to achieve successful immigration reform".

"We need to be a country that follows all laws, but also a country that governs with heart," her statement added.

Democrats can fix their forced family breakup at the Border by working with Republicans on new legislation, for a change! This is why we need more Republicans elected in November. Democrats are good at only three things, High Taxes, High Crime and Obstruction. Sad!

However, critics have pointed out that detaining children separately from their parents is the consequence of a policy announced by Attorney General Jeff Sessions last month to deter new arrivals.

The significant change, analysts say, is the justice department's decision to prosecute parents if they illegally cross the border, even if it is their first offence. The children are not charged with a crime, which means they cannot be jailed together.

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Media captionMigrant boys detained in a former Walmart in Texas

Until this policy was announced, such families were usually subject to civil deportation proceedings, which did not require separation.

What's happening now?

The recent child detentions have resulted in some shelters and foster homes reporting that they are running out of space.

On Sunday, Democratic lawmakers visited shelters and processing facilities in New Jersey and Texas, demanding to see detainees.

"They call it zero-tolerance, but a better name for it is zero-humanity. And there is zero logic to this," Sen Jeff Merkley of Oregon, who organised a visit to Casa Padre detention centre in Brownsville, Texas, told the BBC.

"What we saw is this huge warehouse, it was a super centre for Walmart before, now it's a super detention centre. It's holding almost 1,500 kids inside there."

Vermont congressman Peter Welch said he saw children held "in chain link cages" in a processing facility and one shelter "filled to capacity".

Is the policy working?

In the first two weeks of the new "zero-tolerance" approach, 658 minors - including many babies and toddlers - were separated from the adults that travelled with them, according to US border officials.

In many of the cases, the families have been reunited after the parent was released from detention. However, there are reports of people being kept apart for weeks and even months.

But it is not clear if this new tougher policy will stop the migrants from travelling.

This is because many are fleeing violence and poverty in countries such as Honduras and El Salvador, and staying put is often fraught with dangers.